1. Field of the Invention
The present invention relates to a battery pack, and more particularly, to the structure of a battery pack mounted in a vehicle.
2. Related Art
A battery pack is mounted on a hybrid electric vehicle, a fuel-cell-powered vehicle, or an electric vehicle for storing power to be supplied to a drive motor. A battery pack as a battery stack, and an equipment box with various pieces of equipment used for controlling the battery stack incorporated therein.
FIG. 7 shows a plan view of a related-art battery pack 10. A battery stack 20 is formed by means of stacking a plurality of single cells, each of which is formed from a nickel-metal hydride battery, a lithium ion battery, or the like. An equipment box 40 is located adjacent to the battery stack 20. The equipment box is provided with a control module used for controlling recharging-and-discharging operation of the battery stack 20 and a register, as well as a main relay.
However, in the case of a configuration where the equipment box 40 is located on one side of the battery stack 20, since the battery stack 20 is heavier than the equipment box 40, the centroid of the entire battery pack 10 is biased towards the battery stack 20, which creates an imbalance in the weight of the vehicle when the battery stacked 20 is mounted in the vehicle.
FIG. 8 shows that the battery pack 10 shown in FIG. 7 is mounted in the vehicle 1. When the battery pack 10 is mounted in such a way that the longitudinal direction of the battery pack 10 coincides with the width of the vehicle, the position of centroid Pg of the battery pack 10 deviates to the battery pack 20, thereby deteriorating a lateral weight balance.
Against this backdrop, a method for ensuring a weight balance has hitherto been put forward. For instance, Japanese Patent Laid-Open Publication No. 2004-106807 discloses an attempt to divide into two sub-divisions a battery unit which supplies a drive motor with power. The two split battery units are arranged in the vehicle such that one unit is located on the left side, and the other unit is located on the right side, thereby realizing an attempt to make the weight balance of the vehicle uniform.
FIG. 9 shows the arrangement of a battery. A battery 100 is split into two battery units 100a and 100b. The battery unit 100b is placed rearward of position S below the rearmost seat of a hybrid electric vehicle 250; namely, a position above a tire house 260 and between one vehicle sidewall 210 of a luggage compartment 270 and one interior wall 220. The battery unit 100a is located at a position above the tire house 260 and between the other vehicle sidewall 230 and the other interior wall 240. A low-potential battery 90 is located in close proximity to either the battery unit 100a or the battery unit 100b. In order to achieve balanced distribution of the right and left weights of the hybrid car 250, a DC-DC converter 140 is located at a position between the vehicle sidewall opposite the position where the low-potential battery 90 is placed, and the interior wall. The battery units 100a, 100b are connected in series with the DC-DC converter 140 via a wiring box, and the low-potential battery 90 is also connected in series with the DC-DC converter.
However, dividing the battery into two battery units and placing the battery units on the respective sides of the vehicle leads to an excessive increase in the number of components and a necessity for additional provision of a wiring box used for connecting the two battery units in series with each other. Thus, efforts required to place the divided battery units become useless. Consequently, even when a single enclosure is maintained as a battery pack and mounted in a vehicle, a structure for preventing occurrence of an imbalance in the weight of the vehicle is strongly desired.